Multi-component injection-molded parts are being used increasingly frequently, for example for housings or other parts of electric toothbrushes, electric or mechanical razors, small domestic appliances, blood-pressure measuring devices, clinical thermometers or the like. In some instances, one of the components is a hard plastic and the other component is a soft plastic. The soft plastic component can, for example, form a membrane on the housing of a hard plastic, serve for the actuation of a switch accommodated in the housing, or be formed as a gripping surface on a hard plastic part. Soft plastic components of this type are frequently molded onto a hard plastic housing to improve the handling or grip.
Compact bodies are also used as multi-component injection-molded parts. In cases where one of these components has a coating, special difficulties can arise. For example, when the coating is applied prior to the molding-on of the second component, it can be difficult to effect an intimate connection between the first component and the second component during the injection-molding operation. Such problems can occur, for example, if the a surface portion (e.g., the upper face) of the first component (e.g., a hard plastic) is provided with a metallic coating, followed by molding a second component (e.g., a soft plastic) onto the first component (e.g., by injection-molding), wherein a permanent connection is produced between the first component and the second component. The metallic layer generally prevents an intimate connection between the coated first component and the second component, so that the second component cannot permanently adhere to the first component. One can, for example, mechanically cover the connecting points between the first component and the second component during the coating of the first component. However, permanently connecting the second component to the covered, and uncoated, region of the first component (e.g., using injection-molding), generally results in surface defects at the transitional points between the coated first component and the non-coated second component.